Chapter 13

For each of the following reactions, indicate the Brønsted-Lowry acids and bases. What are the conjugate acid/base pairs? (a) \(\mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{CN}^{-}(a q) \rightleftharpoons \mathrm{HCN}(a q)+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{HNO}_{2}(a q)+\mathrm{OH}^{-}(a q) \rightleftharpoons \mathrm{NO}_{2}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{HCHO}_{2}(a q)+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{CHO}_{2}^{-}(a q)+\mathrm{H}_{3} \mathrm{O}^{+}(a q)\)

According to the Bronsted-Lowry theory, which of the following would you expect to act as an acid? Which as a base? (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) (b) \(\mathrm{HClO}\) (c) \(\mathrm{CN}^{-}\)

According to the Brønsted-Lowry theory, which of the following would you expect to act as an acid? Which as a base? (a) \(\mathrm{CHO}_{2}^{-}\) (b) \(\mathrm{NH}_{4}^{+}\) (c) \(\mathrm{HSO}_{3}^{-}\)

Give the formula of the conjugate acid of (a) \(\mathrm{OH}^{-}\) (b) \(\mathrm{HPO}_{4}{\underline{\phantom{xx}}}^{2-}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{F}^{-}\) (e) \(\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}(\mathrm{OH})_{2}\)

WEB Give the formula of the conjugate base of (a) \(\mathrm{HCO}_{3}^{-}\) (b) \(\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)(\mathrm{OH})_{3}^{-}\) (c) \(\mathrm{HNO}_{2}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}_{2}\) (e) \(\mathrm{H}_{2} \mathrm{SO}_{3}\)

Write a balanced equation showing how the \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) ion can be either a Bronsted-Lowry acid or a Bronsted-Lowry base.

Using the Brønsted-Lowry model, write equations to show why the following species behave as weak acids in water. (a) \(\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{OH}^{+}\) (b) \(\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{3+}\) (c) \(\mathrm{H}_{2} \mathrm{~S}\) (d) \(\mathrm{HPO}_{4}^{2-}\) (e) \(\mathrm{HClO}_{2}\) (f) \(\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}(\mathrm{OH})^{+}\)

Using the Brønsted-Lowry model, write an equation to show why each of the following species produces a basic aqueous solution. (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{NO}_{2}^{-}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (d) \(\mathrm{CO}_{3}{\underline{\phantom{xx}}}^{2-}\) (e) \(\mathrm{F}^{-}\) (f) \(\mathrm{HCO}_{3}^{-}\)

Find the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of solutions with the following \(\left[\mathrm{H}^{+}\right]\). Classify each as acidic or basic. (a) \(6.0 \mathrm{M}\) (b) \(0.33 \mathrm{M}\) (c) \(4.6 \times 10^{-8} M\) (d) \(7.2 \times 10^{-14} M\)

Find the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of solutions with the following \(\left[\mathrm{H}^{+}\right]\). Classify each as acidic or basic. (a) \(1.0 \mathrm{M}\) (b) \(1.7 \times 10^{-4} \mathrm{M}\) (c) \(6.8 \times 10^{-8} \mathrm{M}\) (d) \(9.3 \times 10^{-11} M\)

Calculate \(\left[\mathrm{H}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\) in solutions with the following \(\mathrm{pH}\). (a) \(4.0\) (b) \(8.52\) (c) \(0.00\) (d) \(12.60\)

Calculate \(\left[\mathrm{H}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\) in solutions with the following \(\mathrm{pH}\). (a) \(9.0\) (b) \(3.20\) (c) \(-1.05\) (d) \(7.46\)

Solution 1 has \(\left[\mathrm{H}^{+}\right]=1.7 \times 10^{-2}\). Solution 2 has \(\left[\mathrm{H}^{+}\right]=4.3 \times 10^{-4}\). Which solution is more acidic? Which has the higher pH?

Solution \(\mathrm{X}\) has \(\mathrm{pH}\) 11.7. Solution \(\mathrm{Y}\) has \(\left[\mathrm{OH}^{-}\right]=4.5 \times 10^{-2}\). Which solution is more basic? Which has the higher \(\mathrm{pOH}\) ?

Solution \(\mathrm{X}\) has a \(\mathrm{pH}\) of \(4.35 .\) Solution \(\mathrm{Y}\) has \(\left[\mathrm{OH}^{-}\right]\) ten times as large as solution \(\mathrm{X}\). Solution \(\mathrm{Z}\) has a pH \(4.0\) units higher than that of solution \(\mathrm{X}\). (a) Calculate the ratio of \(\left[\mathrm{H}^{+}\right]\) in solutions \(\mathrm{X}\) and \(\mathrm{Y}\) and solutions \(\mathrm{X}\) and \(\mathrm{Z}\). (b) What is the \(\mathrm{pH}\) of solutions \(\mathrm{Y}\) and \(\mathrm{Z}\) ? (c) Classify each solution as acidic, basic, or neutral.

Solution A has a pH of 12.32. Solution B has \(\left[\mathrm{H}^{+}\right]\) three times as large as that of solution \(A\). Solution \(C\) has a \(\mathrm{pH}\) half that of solution \(\mathrm{A}\). (a) What is \(\left[\mathrm{H}^{+}\right]\) for all three solutions? (b) What is the \(\mathrm{pH}\) of solutions \(\mathrm{B}\) and \(\mathrm{C}\) ? (c) Classify each solution as acidic, basic, or neutral.

Unpolluted rain water has a pH of about 5.5. Acid rain has been shown to have a \(\mathrm{pH}\) as low as \(3.0\). Calculate the \(\left[\mathrm{H}^{+}\right]\) ratio of acid rain to unpolluted rain.

Milk of Magnesia has a pH of \(10.5\). (a) Calculate \(\left[\mathrm{H}^{+}\right]\). (b) Calculate the ratio of the \(\mathrm{H}^{+}\) concentration of gastric juice, \(\mathrm{pH} 1.5\), to that of Milk of Magnesia.

\(\mathrm{m}\) Find \(\left[\mathrm{OH}^{-}\right]\) and the \(\mathrm{pH}\) of the following solutions. (a) \(0.25 \mathrm{~g}\) of \(\mathrm{Ba}(\mathrm{OH})_{2}\) dissolved in enough water to make \(0.655 \mathrm{~L}\) of solution. (b) A 3.00-L solution of KOH is prepared by diluting \(300.0 \mathrm{~mL}\) of \(0.149 \mathrm{MKOH}\) with water. What is the molarity of the diluted solution? What is the effect of a tenfold dilution on the \(\mathrm{pH}\) ?

Find \(\left[\mathrm{H}^{+}\right]\) and the \(\mathrm{pH}\) of the following solutions. (a) \(1.75 \mathrm{~L}\) of a \(37.5 \%\) (by mass) solution \((d=1.00 \mathrm{~g} / \mathrm{mL})\) of \(\mathrm{HCl} .\) What is the \(\mathrm{pH}\) of \(0.175 \mathrm{~L}\) of the same solution? (b) A solution made up of \(22 \mathrm{~g}\) of \(\mathrm{HBr}\) dissolved in enough water to make \(479 \mathrm{~mL}\) of solution. What is the \(\mathrm{pH}\) if the same mass of \(\mathrm{HBr}\) is dissolved in enough water to make \(47.9 \mathrm{~mL}\) of solution?

Find \(\left[\mathrm{OH}^{-}\right],\left[\mathrm{H}^{+}\right]\), and the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of the following solutions. (a) \(0.27 \mathrm{M} \mathrm{Sr}(\mathrm{OH})_{2}\). (b) a solution made by dissolving \(13.6 \mathrm{~g}\) of \(\mathrm{KOH}\) in enough water to make \(2.50 \mathrm{~L}\) of solution.

What is the \(\mathrm{pH}\) of a solution obtained by adding \(5.00 \mathrm{~g}\) of \(\mathrm{HI}\) to \(295 \mathrm{~mL}\) of a \(0.786 M\) solution of \(\mathrm{HNO}_{3} ?\) Assume that the HI addition does not change the volume of the resulting solution.

What is the \(\mathrm{pH}\) of a solution obtained by adding \(13.0 \mathrm{~g}\) of \(\mathrm{NaOH}\) to \(795 \mathrm{~mL}\) of a \(0.200 \mathrm{M}\) solution of \(\mathrm{Sr}(\mathrm{OH})_{2}\) ? Assume no volume change after \(\mathrm{NaOH}\) is added.

Write the ionization equation and the \(K_{\mathrm{a}}\) expression for each of the following acids. (a) \(\mathrm{PH}_{4}{\underline{\phantom{xx}}}^{+}\) (b) \(\mathrm{HS}^{-}\) (c) \(\mathrm{HBrO}_{2}\)

Write the ionization equation and the \(K_{\mathrm{a}}\) expression for each of the following acids. (a) \(\mathrm{HSO}_{3}^{-}\) (b) \(\mathrm{HPO}_{4}{\underline{\phantom{xx}}}^{2-}\) (c) \(\mathrm{HNO}_{2}\)

Calculate \(K_{a}\) for the weak acids that have the following \(\mathrm{pK}_{\mathrm{a}}\) values. (a) \(3.9\) (b) \(10.12\) (c) \(13.07\)

Consider these acids $$\begin{array}{lllll}\hline \text { Acid } & \mathrm{A} & \mathrm{B} & \mathrm{C} & \mathrm{D} \\\K_{\mathrm{a}} & 1.6 \times 10^{-3} & 9 \times 10^{-4} & 2 \times 10^{-6} & 3 \times 10^{-4} \\\\\hline\end{array}$$ (a) Arrange the acids in order of increasing acid strength from weakest to strongest. (b) Which acid has the smallest \(\mathrm{pK}_{\mathrm{a}}\) value?

Rank the following solutions in order of increasing \(\left[\mathrm{H}^{+}\right]\). \(\begin{array}{llll}0.1 & M \mathrm{HBr}, & 0.1 \mathrm{M} \mathrm{HF}, & 0.1 \mathrm{MHCHO}_{2} & 0.1 \mathrm{MHCN}\end{array}\)

The \(\mathrm{pH}\) of a \(0.129 \mathrm{M}\) solution of a weak acid, \(\mathrm{HB}\), is \(2.34\). What is \(K_{\mathrm{a}}\) for the weak acid?

WEB The pH of a \(2.642 M\) solution of a weak acid, \(\mathrm{HB}\), is \(5.32\). What is \(K_{\mathrm{a}}\) for the weak acid?

Caproic acid, \(\mathrm{HC}_{6} \mathrm{H}_{11} \mathrm{O}_{2}\), is found in coconut oil and is used in making artificial flavors. A solution is made by dissolving \(0.450 \mathrm{~mol}\) of caproic acid in enough water to make \(2.0 \mathrm{~L}\) of solution. The solution has \(\left[\mathrm{H}^{+}\right]=1.7 \times\) \(10^{-3} M\). What is \(K_{\mathrm{a}}\) for caproic acid?

Para-aminobenzoic acid (PABA), \(\mathrm{HC}_{7} \mathrm{H}_{6} \mathrm{NO}_{2}\), is used in some sunscreen agents. A solution is made by dissolving \(0.263\) mol of PABA in enough water to make \(750.0 \mathrm{~mL}\) of solution. The solution has \(\left[\mathrm{H}^{+}\right]=2.6 \times 10^{-3} \mathrm{M}\). What is \(K_{\mathrm{a}}\) for PABA?

Butyric acid, \(\mathrm{HC}_{4} \mathrm{H}_{7} \mathrm{O}_{2}\), is responsible for the odor of rancid butter and cheese. Its \(K_{\mathrm{a}}\) is \(1.51 \times 10^{-5} .\) Calculate \(\left[\mathrm{H}^{+}\right]\) in solutions prepared by adding enough water to the following to make \(1.30 \mathrm{~L}\). (a) \(0.279 \mathrm{~mol}\) (b) \(13.5 \mathrm{~g}\)

. Penicillin (MM = \(356 \mathrm{~g} / \mathrm{mol}\) ), an antibiotic often used to treat bacterial infections, is a weak acid. Its \(K_{\mathrm{a}}\) is \(1.7 \times 10^{-3}\). Calculate \(\left[\mathrm{H}^{+}\right]\) in solutions prepared by adding enough water to the following to make \(725 \mathrm{~mL}\). (a) \(0.187\) mol (b) \(127 \mathrm{~g}\)

Uric acid, \(\mathrm{HC}_{5} \mathrm{H}_{3} \mathrm{O}_{3} \mathrm{~N}_{4}\), can accumulate in the joints. This accumulation causes severe pain and the condition is called gout. \(K_{\mathrm{a}}\) for uric acid is \(5.1 \times 10^{-6} .\) For a \(0.894 M\) solution of uric acid, calculate (a) \(\left[\mathrm{H}^{+}\right]\) (b) \(\left[\mathrm{OH}^{-}\right]\) (c) \(\mathrm{pH}\) (d) \% ionization

Barbituric acid \(\left(K_{\mathrm{a}}=1.1 \times 10^{-4}\right)\) is used in the manufacture of some sedatives. For a \(0.673 \mathrm{M}\) solution of barbituric acid, calculate (a) \(\left[\mathrm{H}^{+}\right]\) (b) \(\left[\mathrm{OH}^{-}\right]\) (c) \(\mathrm{pH}\) (d) \% ionization

Phenol, once known as carbolic acid, \(\mathrm{HC}_{6} \mathrm{H}_{5} \mathrm{O}\), is a weak acid. It was one of the first antiseptics used by Lister. Its \(K_{\mathrm{a}}\) is \(1.1 \times 10^{-10} .\) A solution of phenol is prepared by dissolving \(14.5 \mathrm{~g}\) of phenol in enough water to make \(892 \mathrm{~mL}\) of solution. For this solution, calculate (a) \(\mathrm{pH}\) (b) \% ionization

Benzoic acid \(\left(K_{\mathrm{a}}=6.6 \times 10^{-5}\right)\) is present in many berries. Calculate the \(\mathrm{pH}\) and \(\%\) ionization of a \(726-\mathrm{mL}\) solution that contains \(0.288 \mathrm{~mol}\) of benzoic acid.

There are \(324 \mathrm{mg}\) of acetylsalicylic acid \((\mathrm{MM}=180.15 \mathrm{~g} / \mathrm{mol})\) per aspirin tablet. If two tablets are dissolved in water to give two ounces \(\left(\frac{1}{16}\right.\) quart) of solution, estimate the \(\mathrm{pH} . K_{\mathrm{a}}\) of acetylsalicylic acid is \(3.6 \times 10^{-4}\).

Write the overall chemical equation and calculate \(K\) for the complete ionization of oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\)

Consider the diprotic acid \(\mathrm{H}_{2} \mathrm{~A}\). For the first dissociation of \(\mathrm{H}_{2} \mathrm{~A}, K_{\mathrm{al}}=\) \(2.7 \times 10^{-4} .\) For its second dissociation, \(K_{\mathrm{a} 2}=8.3 \times 10^{-7} .\) What is the \(\mathrm{pH}\) of a \(0.20 \mathrm{M}\) solution of \(\mathrm{H}_{2} \mathrm{~A}\) ? Estimate \(\left[\mathrm{HA}^{-}\right]\) and \(\left[\mathrm{A}^{2-}\right]\).

Phthalic acid, \(\mathrm{H}_{2} \mathrm{C}_{8} \mathrm{H}_{4} \mathrm{O}_{4}\), is a diprotic acid. It is used to make phenolphthalein indicator. \(K_{\mathrm{al}}=0.0012\), and \(K_{\mathrm{a} 2}=3.9 \times 10^{-6} .\) Calculate the \(\mathrm{pH}\) of a \(2.9 \mathrm{M}\) solution of phthalic acid. Estimate \(\left[\mathrm{HC}_{3} \mathrm{H}_{4} \mathrm{O}_{4}^{-}\right]\) and \(\left[\mathrm{C}_{8} \mathrm{H}_{4} \mathrm{O}_{4}^{2-}\right]\)

Ascorbic acid, \(\mathrm{H}_{2} \mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{6}\), also known as vitamin \(\mathrm{C}\), is present in many citrus fruits. It is a diprotic acid with the following \(K_{\mathrm{a}}\) values: \(K_{\mathrm{al}}=7.9 \times 10^{-5}\); \(K_{\mathrm{a} 2}=1.6 \times 10^{-12}\). What is the \(\mathrm{pH}\) of a \(0.63 \mathrm{M}\) solution of ascorbic acid? Estimate \(\left[\mathrm{HC}_{6} \mathrm{H}_{6} \mathrm{O}_{6}^{-}\right]\) and \(\left[\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{6}{\underline{\phantom{xx}}}^{2-}\right]\).

Write the ionization expression and the \(K_{b}\) expression for \(0.1 M\) aqueous solutions of the following bases. (a) \(\mathrm{F}^{-}\) (b) \(\mathrm{HCO}_{3}^{-}\) (c) \(\mathrm{CN}^{-}\)

Find the value of \(K_{b}\) for the conjugate base of the following organic acids. (a) picric acid used in the manufacture of explosives; \(K_{\mathrm{a}}=0.16\) (b) trichloroacetic acid used in the treatment of warts; \(K_{\mathrm{a}}=0.20\)

Find the value of \(K_{\mathrm{a}}\) for the conjugate acid of the following bases. (a) pyridine, a pesticide; \(K_{\mathrm{b}}=1.5 \times 10^{-9}\) (b) aniline, an important dye intermediate; \(K_{\mathrm{b}}=3.8 \times 10^{-10}\)

Codeine (Cod), a powerful and addictive painkiller, is a weak base. (a) Write a reaction to show its basic nature in water. Represent the codeine molecule as Cod. (b) The \(K_{\mathrm{a}}\) for its conjugate acid is \(1.2 \times 10^{-8} .\) What is \(K_{\mathrm{b}}\) for the reaction written in (a)? (c) What is the \(\mathrm{pH}\) of a \(0.0020 \mathrm{M}\) solution of codeine?

Consider sodium acrylate, \(\mathrm{NaC}_{3} \mathrm{H}_{3} \mathrm{O}_{2} . K_{\mathrm{a}}\) for acrylic acid (its conjugate acid) is \(5.5 \times 10^{-5}\). (a) Write a balanced net ionic equation for the reaction that makes aqueous solutions of sodium acrylate basic. (b) Calculate \(K_{b}\) for the reaction in (a). (c) Find the \(\mathrm{pH}\) of a solution prepared by dissolving \(1.61 \mathrm{~g}\) of \(\mathrm{NaC}_{3} \mathrm{H}_{3} \mathrm{O}_{2}\) in enough water to make \(835 \mathrm{~mL}\) of solution.

The \(\mathrm{pH}\) of a household ammonia cleaning solution is \(11.68\). How many grams of ammonia are needed in a 1.25-L solution to give the same pH?

Write formulas for two salts that (a) contain \(\mathrm{Ni}^{3+}\) and are acidic. (b) contain \(\mathrm{Na}^{+}\) and are basic. (c) contain \(\mathrm{ClO}_{4}^{-}\) and are neutral. (d) contain \(\mathrm{NH}_{4}{\underline{\phantom{xx}}}^{+}\) and are acidic.